With the constant development of the touch screen technology, Touch and Display are no longer two independent forms of technology. More and more makers of the Thin Film Transistor-Liquid Crystal Display (TFT-LCD) start to try to combine Touch and Display, such as In-Cell Touch, One Glass Solution (OGS), On-Cell Touch and Hybrid In-Cell Touch. The touch technology of combining Touch and Display seems to race to emerge.
In comparison with OGS, On-Cell Touch or Hybrid In-Cell Touch panels, the In-Cell Touch panel possesses advantages of lighter, lesser process flow and more stable structure. The In-Cell Touch is to integrate all the touch control circuits inside the LCD without additionally being attached Touch Sensor Glass or more On-Cell process on the LCD. Accordingly, the integration and the shortening of the production flow and the production time can be achieved, which can make bigger profits for the LCD makers. Meanwhile, by utilizing the stepper of high resolution, the In-Cell Touch panel with higher resolution can be realized and the Moire interference can be effectively prevented. Thus, the In-Cell Touch panel will be the mainstream direction for the development of the small and medium size touch control panel in the future.
In the production process of the In-Cell Touch panel, the electrodes and the wirings for touch control display have to be designed on the array substrate, such as the Low Temperature Poly-silicon (LTPS) array. The array process is much more complicated than the process of the traditional amorphous silicon (a-Si). The integration of the In-Cell Touch and the LTPS does not only make the array process more complicated, longer production period but also has more strict demands for the array process.
The In-Cell Touch panels can be divided into the self capacitance type and the mutual capacitance type. Both need the connection electrodes for coupling the pixel areas. Thus, one or more Photo Engraving Process (PEP) is added for manufacturing the connection electrodes for coupling the pixel areas (or so called Metal3 or M3) and the corresponding insulation layer. The added M3 manufacture process can create risk to the yield of the product because the etching process of M3 may cause the Mura defects. However, in the In-Cell Touch technology, M3 has to be utilized for coupling the pixel areas. Therefore, the yield promotion of the In-Cell Touch panel is restricted in a certain extent.